The basic working system of eddy current displacement sensor is composed of measured body, probe, extension cable and preprocessor. The preprocessor generates high-frequency oscillating current into the probe coil through the extension cable, and the coil will generate axial magnetic field. When the measured metal body is close to the magnetic field, eddy current will be generated on the measured metal surface (the strength of the eddy current will change with the change of the distance between the probe and the measured body surface), thus causing the Q value of the coil to change. When the distance is small, the eddy current effect is strong and the coil Q value is small. When the distance is large, the eddy current effect is weak and the coil Q value is large. In practical application, the change of coil Q value is converted into the change of voltage by detecting and amplifying by the preprocessor. Convert the mechanical displacement (clearance) value to the voltage value.